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fix: combine prerendered trailing slash redirects into as few Vercel routes as possible - #17523
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added this pull request to stack #17524
October 22, 2026 18:17
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Install the latest version of pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/0b7b25486d1115a4e24bcb5d9e4adac8ab330333Open in |
🦋 Changeset detectedLatest commit: 0b7b254 The changes in this PR will be included in the next version bump. This PR includes changesets to release 2 packages
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Stacked on #17522, which covers apps where every route uses the same
trailingSlash. This PR makes the fallback for everything else (mixed options and'ignore') much smaller.Currently the adapter adds two routes per prerendered page. One of them,
{ src: path, dest: counterpart }, is unnecessary: Vercel strips trailing slashes before it looks up a static file, so/foo/already findsfoo. Worse, because that route doesn'tcontinue, it stops the routes after it from running. For example, prerendered pages skipped the route that sets the skew protection cookie (going by the proxy source; I haven't tested this with skew protection turned on).The redirects themselves were also buggy:
/blog/café/never matched its redirect./v1.2/also matched/v1x2/.What changed
^/(blog/a|blog/b|…)/$→/$1. A new route starts whenever one gets close to Vercel's 4096-character limit onsrc. A thousand blog posts now take about 7 routes instead of 2,000.encodeURI, the same way Kit's prerenderer does it, and regex-escaped. The routes arecaseSensitive, matching Kit's router.There's one small gap left: a client that sends lowercase hex escapes (
%c3%a9) won't match a redirect. The page is still served, it just isn't redirected. Browsers send uppercase.Tests
basichas new dynamic prerendered routes for both trailing slash modes, with build and platform tests. The redirect test fails onmainfor thecafépage.